Collaborative Research: Frustration, glassiness and spin liquids: from dirty to pristine materials

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

Non-technical abstract Currently, immense global experimental efforts are directed at finding quantum spin liquids (QSLs), a theoretically-predicted state of magnetic materials in which the spins, or atom-size bar-magnets, exhibit liquid-like properties down to the lowest possible temperatures. QSLs can be efficiently used to create quantum bits, “qubits”, as they can store information encoded simultaneously in the states of multiple spins, and hence protected from local noise. Thus, QSLs hold great promise as a platform for future computing and communication technology. A present barrier to their realization is randomly located impurities and defects that can convert a QSL into another state of matter, “spin glass”, in which the spins freeze in random orientations, similar to how silicon atoms possess random positions in window glass. This research investigates the effect of impurities and defects on the fundamental properties of geometrically frustrated magnets, the largest class of materials in which QSLs are being sought. Through systematically controlling defects during material synthesis, and theoretically modeling the resulting behavior, the team is laying the foundations for future engineering of QSL-based devices. The broader impacts of this research are both the development of synthesis methods for reducing defects in crystalline specimens and the theoretical understanding that will inform future processing endeavors. In addition, the research helps train junior researchers directly involved in the project, as well as the broader community through instructional media and data that are accessible on open-source platforms such as the NSF’s Crystal Sample Archive. Technical abstract This research is a combined experimental and theoretical effort to systematically investigate the effect of quenched disorder on collective magnetism in geometrically frustrated (GF) materials and to determine the synthesis barriers to obtaining pure materials. The research includes synthesis of materials spanning the entire range of spin density from dilute spin, to concentrated disordered spins, to dilute impurities, en route to ultra-pure materials. Part of the work uses quenched disorder as a probe of fundamental properties of GF magnetism. The measurements of the thermodynamic properties of disordered GF materials aim to uncover microscopic Hamiltonians of GF systems, reveal possible universality classes of disorder-induced spin-glass transitions, investigate the origin of the recently discovered “hidden energy scale” in these systems and reveal the nature of elementary excitations in them. The work includes theoretical calculations of the thermodynamic manifestations of the microscopic details of the Hamiltonians, exploring the interplay of different types of disorder in GF media and constructing models for the “hidden energy scale” and the behavior of heat capacity in GF magnets, which is used to make prediction and explain experimental data. Part of this research may result in obtaining materials that exhibit strong quantum-spin-liquid behavior and demonstrating the irrelevance of quenched disorder in them. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.